The present invention relates to a method and a device for measuring the tensile stress distribution in a metal strip between two roll stands or between a roll stand and a coiler. The present invention can also be used in conjunction with S rolls and blooming stands.
In rolling metal strips, in particular in cold rolling, the tensile stress distribution in the metal strip across the width of the metal must be determined on-line, i.e., it must be measured routinely because the tensile stress distribution is the deciding factor in regulating the flatness of a metal strip.
For example, in a conventional system, the metal strip can be guided over a measuring roll, i.e., a segmented deflection roller which has piezoelectric pressure sensors at intervals of approximately 2-5 cm. The force acting on the sensors is a measure of the tensile stress distribution. This is a contact method which can therefore leave impressions in the metal; furthermore, it is subject to wear and is thus maintenance intensive. However, one particular disadvantage of this method is that only incomplete measured values are obtained for the edge area of the metal strip, e.g., if the latter covers a piezoelectric pressure sensor only partially. Because of the great distortion of a measured value when there is only partial coverage, these measured values are discarded so that no measured values are available for the tensile stress in the edge area.
An object of the present invention is to provide a method and a device for avoiding the disadvantages described above.
According to the example embodiment of the present invention, to measure the tensile stress distribution in a metal strip, the metal strip is deflected, and the deflection of the metal strip is measured by several sensors arranged across the width of the metal strip, with the tensile stress distribution in the metal strip being calculated as function of the deflection of the metal strip, and with correction of the measured values of sensors located in the edge area of the metal strip whose measurement range is not covered completely by the metal strip i.e., extends beyond the metal strip.
In an advantageous embodiment, at least one edge of the metal strip is determined by the sensors.
In another advantageous embodiment of the present invention, the metal strip is deflected periodically, and at least one edge of the metal strip is determined from a time average of the measured values supplied by the sensors over time.
In another advantageous embodiment of the present invention, the metal strip is deflected periodically, and the tensile stress distribution is determined from the amplitude of the measured values supplied by the sensors.
In another advantageous embodiment of the present invention, the measured values of sensors in the edge area of the metal strip whose measurement range is not covered completely by the metal strip are corrected as a function of the position of the edge of the metal strip.
In another advantageous embodiment of the present invention, the measured values of sensors in the edge area of the metal strip whose measurement range is not covered completely by the metal strip are corrected on the basis of stored calibration curves.